Integrated microbiota and multi-omics analysis reveal the differential responses of earthworm to conventional and biodegradable microplastics in soil under biogas slurry irrigation.

As one of the promising alternatives of conventional plastic mulching film (C-PMF), biodegradable plastic mulching films (B-PMF) were employed in agronomy production to alleviate the environmental burden of C-PMF. However, information regarding the potential toxicity effects of biodegradable microplastics (MPs) in soil still in scarcity, and the available findings were found to be controversial. Additionally, little is known about the molecular toxicity effects of conventional and biodegradable MPs on terrestrial organisms. Thus, 5 % (w/w) biodegradable (polylactic acid, PLA) and conventional (polyvinylchloride, PVC; low-density polyvinylchloride, LDPE) MPs were employed to assess the toxicity effects on Eisenia fetida in agricultural soil with biogas slurry irrigation. In the present study, transcriptomic, metabolomic profiles and individual indexes were selected to reveal the toxicity mechanisms from molecular level to the individual response. Furthermore, dysbiosis of bacterial community in gut was also investigated for obtaining comprehensive knowledge on the MPs toxicity. At the end of the exposure, the number of survival earthworms after MPs exposure was significantly reduced. Compared with the initial body weight, PLA and LDPE increased the biomass of earthworms after MPs exposure, while no significant influence on the biomass was observed in PVC treatment. Microbacterium, Klebsiella and Chryseobacterium were significantly enriched in earthworm gut after PLA, PVC and LDPE exposure, respectively (p < 0.05). Transcriptomic and metabolomic analysis revealed that PLA exposure induced neurotransmission disorder and high energetic expenditure in earthworms. However, PVC and LDPE inhibited the nutrient absorption efficiency and activated the innate immunity responses of earthworms. The PLS-SEM results showed that the effects of MPs were dominated by the polymer types, and hence, significantly and directly influence the gut bacterial community of earthworms. This study provides a better understanding of the similarities and discrepancies in toxicity effects of biodegradable and conventional MPs from the perspectives of individual, gut bacterial community, transcriptome and metabolome.

Zhao Y ，Jia H ，Deng H ，Ge C ，Xing W ，Yu H ，Li J ... -  《-》

Response of earthworms to microplastics in soil under biogas slurry irrigation: Toxicity comparison of conventional and biodegradable microplastics.

As a reliable environment-friendly alternative, biodegradable plastic mulching films have been introduced into agricultural practice to reduce the adverse threats posed by conventional plastic products. Information regarding whether potential untoward effects of biodegradable plastics exist in soil and how strong are such effects on terrestrial organisms, however, still remains unknown. This study examined differences in the responses of earthworm, represented by Eisenia fetida, to exposure to biodegradable (PLA: polylactic acid) and conventional microplastics (PVC: polyvinylchloride, LDPE: low-density polyethylene) in soil with biogas slurry irrigation. Mortality, growth, histopathology and biochemical enzymes of the earthworms exposed to different concentrations of microplastics (5, 20 and 50 g/kg wet weight of soil, respectively) were investigated after 28 days of incubation in the experiment. The obtained results showed that the ecotoxicity of microplastics (MPs) to earthworms was time-dependent. Regardless of MPs type, continuous exposure to MPs at the concentration of 50 g/kg induced mucous vacuolization, longitude muscle disorder, and granular lipofuscin-like deposits generation in the epithelium. Moreover, tissue fibrosis and cavity formation were also observed in intestinal tissue. The presence of MPs stimulated the oxidative stress system of the earthworms, as indicated by the enhancement of malonaldehyde (MDA) content in vivo. The antioxidative defense system in earthworms was supposed to collapse at the MPs concentration of 50 g/kg after 28 days of exposure. Interestingly, PLA exhibited similar ecotoxicity effects with LDPE, which might violate the original intention of biodegradable plastics with less harmful or nontoxic influence on the terrestrial biotas. Thus, knowledge regarding the molecular and genetic mechanisms of the earthworms in soil containing biodegradable plastics should be further explored to better understand the risk posed by biodegradable plastics in the agroecosystem.

Zhao Y ，Jia H ，Deng H ，Xing W ，Feng D ，Li J ，Ge C ，Yu H ，Zhang Y ，Chen H ... -  《-》

Reproduction, growth and oxidative stress in earthworm Eisenia andrei exposed to conventional and biodegradable mulching film microplastics.

Plastic contamination in agricultural soils has become increasingly evident. Plastic mulching films are widely used in agricultural practices. However, the increased use of biodegradable plastics has, to some extent, replaced their non-degradable counterparts. The fragmentation of plastics generates microplastics (MPs), posing risk to soil functions and organisms. In this study the effects of low-density polyethylene microplastics (PE-MP) and polybutylene adipate terephthalate biodegradable microplastics (PBAT-BD-MP) originating from mulching films on the earthworm Eisenia andrei were studied. The earthworms were exposed to seven concentrations (0, 0.005, 0.05, 0.1, 0.5, 1, and 5 % w/w) based on environmentally relevant levels and worst-case scenarios on soil contamination. Survival, growth, reproduction, and biomarkers for oxidative stress [superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione S-transferase (GST), glutathione (GSH), and lipid peroxidation (LPO)] were analysed. Additionally, the Integrated Biomarker Response Index (IBR) was calculated to assess the overall oxidative stress status of the earthworms. Results showed that PE-MP exposure slightly decreased the biomass of the earthworms towards higher concentrations, whereas PBAT-BD-MPs induced growth at lower concentrations. MPs did not have a significant effect on Eisenia andrei reproduction; however, a slight negative trend was observed in juvenile production with increasing PE-MP concentrations. Both PE-MP and PBAT-BD-MP affected antioxidant system, PE-MPs with changes in CAT and GR levels and PBAT-BD-MPs inducing effects on SOD and LPO levels. Additionally, both MPs exhibited effects on soil parameters, resulting in increased soil pH and water-holding capacity at 5 % concentration. Changes in soil parameters can further affect soil organisms such as earthworms. This study provides understanding of the ecotoxicological effects of conventional and biodegradable microplastics on the earthworm Eisenia andrei. It also shows that MP particles of both conventional and biodegradable mulching films induce oxidative stress, considered as an early-warning indicator for adverse ecological effects, in environmentally relevant concentrations.

Forsell V ，Saartama V ，Turja R ，Haimi J ，Selonen S ... -  《-》

Effects of conventional versus biodegradable microplastic exposure on oxidative stress and gut microorganisms in earthworms: A comparison with two different soils.

The ecotoxicity of microplastics (MPs) to soil animals is widely recognized; however, most studies have only focused on conventional MPs. This study compared the effects of various concentrations (0.5%, 1%, 2%, 5%, 7%, and 14%, w/w) of polyethylene (PE) and biodegradable polylactic acid (PLA) MPs on oxidative stress and gut microbes in Eisenia fetida (E. fetida) from two different soils (black and yellow soils). The results indicated that the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione S-transferase (GST), and acetylcholinesterase (AchE) decreased after exposure to PE and PLA MPs for 14 days, whereas malondialdehyde (MDA) levels increased. This level of decrease or increase exhibited a "decrease-increase" trend with increasing MP exposure doses. After 28 days, the activities of SOD, CAT, POD, AchE, and GST increased, whereas MDA levels decreased, and the level of increase or decrease increased with increasing MP dose. The integrated biological response index revealed that the toxic effects of MPs were concentration-dependent, and MP concentration was more important than MP type or soil type. The toxicity of PE MPs was generally higher than that of PLA MPs on day 14, with no significant difference on day 28. Moreover, MPs did not alter the dominant gut microbiota of E. fetida, but altered the relative abundances of Actinobacteriota, Bacteroidota, Ascomycota, and Rozellomycota. Furthermore, different gut microbial phyla exhibited discrepant responses to MPs. Our results demonstrated that both conventional and biodegradable MPs induced oxidative stress in E. fetida, and biodegradable MPs showed no less toxicity compared to conventional MPs. Additionally, MP-induced toxic effects did not differ significantly between black and yellow soils, suggesting that MP-induced toxic effects were less affected by soil type.

Yu H ，Shi L ，Fan P ，Xi B ，Tan W ... -  《-》

Earthworms mediate the influence of polyethylene (PE) and polylactic acid (PLA) microplastics on soil bacterial communities.

Lu S ，Hao J ，Yang H ，Chen M ，Lian J ，Chen Y ，Brown RW ，Jones DL ，Wan Z ，Wang W ，Chang W ，Wu D ... -  《-》